An application of population kinetics analysis to estimate pharmacokinetic parameters of sodium tungstate after multiple-dose during preclinical studies in rats

The purpose of this study was to use a population approach in the preclinical development program of sodium tungstate in the rat in order i) to compute individual pharmacokinetic parameters of this compound after repeated oral administrations. until the 4-week toxicology study, using an empirical Bayes methodology; and ii) to study the influence of the administered dose, of the gender and of the duration of treatment on the pharmacokinetic parameters. Four studies were used representing a mixture of single intravenous administration and multiple oral administrations. The treatment duration ranged from 7 to 28 days. Intravenous dose was 9 mg/kg. three different oral doses were tested. 50, 100 and 200 mg/kg/day. Plasma concentration profiles versus time were compatible with a two-compartment model. A significant gender effect was found on bioavailability. The duration of treatment and the administered dose did not significantly explain part of the interindividual variability of pharmacokinetic parameters. The absorption of tungsten was rapid (1-3 hr). Total plasma clearance and elimination half-life averaged 2.8 ml/min./kg and 3.04 hr in males, and 3 ml/min./kg and 2.74 hr in females. The bioavailability was on an average 70%; being significantly higher in females than in males (0.79 versus 0.61). This compartmental approach should be considered as complementary to the usual non-compartmental approach used for analysis of preclinical data and should be a valuable tool to characterise the pharmacokinetic/pharmacodynamic behaviour of a drug.